Mine
by Tiana-P
Summary: At first, he was glad to see his protege, Alex, back in town. Then he introduced him to the real Nikki Heat, his Detective Beckett. Rick's not so happy anymore. Spoilers for ep 3x21. Oneshot


**_A/N: Heya! This is my second Castle fic ever and of the day. I've never written two fics in a day, but I just watched a sneak peek for this episode [airing 12th April '11] and it just had to be written. So please R&R and I do hope you'll enjoy!_**

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><p>"Is Alex short for Alexander, by any chance?"<p>

"Yeah. Yeah, it is, actually. Why?" The young protégé replied with a wide smile at the detective's question. Beckett couldn't help but to smile back at the young man, if only it was out of politeness.

"No reason." She shrugged, turning back to the board where she was drawing the timeline for their latest case. Alex Gordon stood next to her, slightly unnerving even though she was use to it from all the times that Castle had, and still did, the same. Feeling his eyes burn into her temple, Beckett spared him a glance from the side of her eyes to see him cross his arms and lean lightly against the board itself, almost as if he was waiting for her to carry on. "There was this case. It's stupid really."

"Can't have been if you still remember it." Alex told her and Beckett turned to face him, replacing the lid back onto the black marker to pick up a red one.

"There was this psychic who told me that an Alexander would be important to me." She told him with a small shake of the head and smile, turning back to the board. "Said that he might save my life or something."

"Oh, really?" Alex laughed and Beckett rolled her eyes. There was a similarity between him and Castle that was very hard to miss. Then again, it could have just be a trait for all mystery writers. "In that case, Detective, I shall keep an eye out for any impending danger." She laughed at his words.

"You do that." She told him lightly, taking a step back to look at the board before swapping the red for blue to write the details of the case.

"Do what?" Castle's voice made her jump. She hadn't heard him approach, but accepted the coffee he slipped into her hand gratefully.

"Hmm?" She murmured, looking at him over the rim of her mug as she took a grateful sip.

"You said Alex should do something." He clarified, eyes jumping between the two of them and Beckett raised an eyebrow at his suspicious look that overtook his normally relaxed features. Placing her mug onto her desk, she opened her mouth to explain but was beaten to it by the man in question.

"Beckett was just telling me how a psychic told her once that an Alexander would save her life." Alex explained matter-of-factly. Castle's eyes widened and Beckett smiled back shyly at him when they turned onto her. "So I said I'd do my best."

"Uh huh." Castle managed to get out, still staring at his partner who had turned back to the murder board.

"Hey, where did you get that espresso from? I could really do with a fix." Alex said suddenly, clearly not sensing the sudden tension between the other two people with him.

"Break room." He informed him and Alex made his way over almost immediately

"I thought you didn't believe in psychics?" Castle stated as soon as he was out of earshot. Beckett didn't even pause with what she was writing as she replied.

"I don't." She murmured. "It just came to mind. I shouldn't have brought it up."

"I thought we agreed that I was that Alexander?" He asked her, slightly petulantly. Beckett froze mid-word.

"No, I think _you_ agreed on that." She told him as she carried on writing. "Like I said, I don't believe in that drabble."

"Good!" Castle said, crossing his arms strictly and nodding. "You're _my _partner. _My _muse."

"Don't call me a muse." Beckett muttered once again. He had been good and not done so any previous times after she had reprimanded him the first and only time he had called her a 'muse' to her face.

"Inspiration, then." He amended with a huff, settling at the edge of her desk in a mood. "Still mine."

"C'mon, Castle. You can't say that you don't like to share. God knows you share more than is necessary on a daily basis." Beckett teased, turning to face him and breaking into a smile at the grumpy look on his face. If there was ever a day where he actually looked like a nine year old, it was right then. And she wouldn't ever admit it in fear of enlarging his ego, but it was actually adorable.

"I can share a lot of things. But not you." He agreed with a nod before backtracking with his words when she turned to him with a shocked and a little worried look. "Wait, that didn't come out how I meant."

"Uh huh?" She asked, putting him on the spot until he came up with a better explanation.

"What I meant was, I don't share my muses- Inspiration!" He quickly rectified, only for her to shoot him a questioning look instead.

"Mus_es_? Plural?" Beckett asked wit ha faux hurt tone. "I thought I was your only one, Castle. Have you been cheating on me and my inspiration?"

"Never!" Castle gasped in horror, failing at keeping back his smile as he did so. "I'd never commit such a- a- an atrocity."

"Hmm... For a moment there, I was slightly relieved. Thought I might have found a way of finally getting rid of you." She sighed dramatically and shook her head.

"Nope, sorry. I'll always be yours." Beckett scoffed playfully at his words. "And you, mine."

His words sent her a strange sense of reassurance. Any snappy or teasing reply flew straight out of her head and instead she settled for a soft smile that he mirror. Castle had told her 'always' many times before, but it had never been in the context of belonging before. Because that was what had stopped her suddenly; a strange, wonderful, awkward sense of belonging. Even if 'always' didn't quite last that long, at least she had proof that once, she did in fact belong somewhere.

"Hey, guys, I think-" Alex broke them both out of their moment as he approached them again. "Am I interrupting something?"

"No." They both replied at the same time. Castle averted his eyes to the board to take in the information about the case whilst Beckett turned to the file she was writing from.

"Anyway, I was just standing there making a coffee, and I realised something. Something that I should have realised earlier." Alex carried on, not waiting for the other two to reply. "All great writers have books based on people. Either themselves or others."

"Are you saying what I think you're saying?" Castle asked, heading snapping towards him so quickly that Beckett was surprised he hadn't gotten whiplash.

"Well, I haven't really had much of a life so far to write about. And after my _fantastic _début novel, people are calling me 'the next Richard Castle' anyway." He carried on. She stifled a laugh by pressing her fingers to her lips at the look of astonishment on Castle's face. She almost felt sorry for him and his dumbstruck ego. "So I need myself a muse. A Detective Beckett of my own."

"Yeah, well- You see- The thing is-" Castle faltered, not sure exactly what he wanted to say. Taking in a deep breath, he relaxed and tried again. "Muses can't really be found. They find you."

"Or arrest you." Beckett supplied, turning back to the board once more with a smirk.

"Or that." He agreed, smirking back knowingly, leaving Alex out in the cold about whatever secret they were clearly sharing. "But- Yeah. And Beckett's mine."

"Castle." She said warningly. Even without turning around, he knew she was rolling her eyes at him.

"I'm just saying." He defended himself.

"Nah, that's cool, Rick. Stealing another writer's muse is like... Like stealing another songwriter's lyrics." Alex said and Castle nodded, glad that they had came to an understanding, if only on the muse front. He wasn't too sure how long it would take to get a truce on the partner front. "Right, so I'm going to go find that muse. Or let her find me. I'll see you later, yeah?"

"See you, Alex." Castle called after him after Beckett had bid him good bye too. They fell back into silence; her finishing off the murder board while he contemplated possible methods of keeping Kate Beckett as his own. "Hey, what would you say if I copyrighted you? Is that even possible? It sounds like it is. Or should be..."

Beckett stared at him in confusion before rolling her eyes and brushing it off. After nearly 3 years, she wasn't sure why she was still surprised. Walking up to him, she lifted her hand and flicked him sharply in the middle of his forehead before walking past him to sit down.

"I'll take that as a no to the copyrighting then." Castle sighed even as a smile tugged at his mouth. As much as she pretended to hate it, he knew that Beckett had now grown use to the fact that people knew her as the inspiration behind Nikki Heat to the point that she could even joke about it. But the bit that had stuck with him the most was the fact that despite her hatred of his calling her his muse, she hadn't once argued the fact that he had called her '_mine'_. It was definitely a step in the right direction.

...


End file.
